1. Field of the Invention
The present invention relates to a digital information processing system and more particularly, to a digital information processing system with a copy protection subsystem, which plays back a stream of multiplexed video, audio, and data packets of programs or services that have been packet-multiplexed in conformity with the standard given by the Moving Picture coding Experts Group (MPEG) (i.e., the MPEG standard), while preventing the programs or services from being copied illegally.
2. Description of the Prior Art
To protect the programs or services from being copied illegally in digital information processing systems of this sort, conventionally, several copy protection methods have been developed and reported.
For example, (a) some protection scheme is mixed into or added to the analog video, audio, and data signals of a program or programs to be copy-protected, (b) a specific protection code is additionally mixed into or added to the digital video, audio, and data signals of a program or programs to be copy-protected, or (c) the digital video, audio, and data signals of a program or programs to be copy-protected are scrambled.
FIG. 1 shows a conventional broadcasting receiver apparatus 161 designed for receiving toll broadcasting waves, which is disclosed in the Japanese Non-Examined Patent Publication No. 3-147490 published in 1991.
In the conventional broadcasting receiver apparatus 161, as shown in FIG. 1, a demultiplexer 162 demultiplexes an audio signal and a related information signal that have been multiplexed and scrambled, thereby outputting a scrambled audio signal 163 to an audio descrambler 174 and a scrambled related information signal 164 to a decoder 165.
The decoder 165 decodes or deencrypts the related information signal 164 thus inputted using a key signal 166, thereby outputting an agreement signal 167 to an agreement comparator circuit 169 and an initializing signal 168 to a pseudo random-number generator 171.
The agreement comparator circuit 169 compares the content of the agreement signal 167 to the content of the built-in agreement of the receiver apparatus 161, and outputs a comparison result signal 170 to the pseudo random-number generator 171 and a control signal 181 to a mixer 180.
According to the initializing signal 168 and the comparison result signal 170 thus received, the pseudo random-number generator 171 generates a sequence 172 of pseudo random numbers for audio signals and a sequence 173 of pseudo random numbers for video signals. The pseudo random-number sequence 172 for audio signals and the pseudo random-number sequence 173 for video signals are inputted into the audio descrambler 174 and a video descrambler 175, respectively.
The control signal 181 from the agreement comparator circuit 169 is used to control the mixer 180.
The audio descrambler 174 descrambles the scrambled audio signal 163 and outputs an analog audio signal 177 which is the same as the original audio signal. The analog audio signal 177 is then reproduced or played back by an audiovisual playback system (not shown).
The video descrambler 175 descrambles a scrambled video signal thus received and outputs an analog video signal 176 to the mixer 180. The analog video signal 176 is the same as the original video signal.
A copy-protection signal generator 178 generates a copy protection signal 179 and supplies the signal 179 to the mixer 180. According to the control signal 181 outputted from the agreement comparator circuit 169, the mixer 180 performs a mixing operation of the copy protection signal 179 with the analog video signal 176 outputted from the video descrambler 175.
Specifically, when the agreement signal 167 from the decoder 165 does not accord with the content of the built-in agreement of the receiver apparatus 161, the mixer 180 performs the mixing operation of the copy protection signal 179 with the analog video signal 176 according to the control signal 181. Then, the mixer 180 outputs the mixed video signal 176 to the audiovisual playback system (not shown) as a video signal 182.
On the other hand, when the agreement signal 167 from the decoder 165 accords with the content of the built-in agreement of the receiver apparatus 161, the mixer 180 does not perform the mixing operation of the copy protection signal 179 with the analog video signal 176 according to the control signal 181. In this case, therefore, the mixer 180 outputs the inputted video signal 176 without any change as the video signal 182 to the audiovisual playback system (not shown).
With the conventional receiver apparatus 161 having the above-described configuration, a control or copy-protection bit to enable or disable the copy-protection function is provided in the related information signal in advance. The related information signal is encrypted in a transmitter and then transmitted by the transmitter.
In the receiver apparatus 161 shown in FIG. 1, the related information signal is demultiplexed by the demuliplexer 162 and then, deencrypted by the decoder 165 using the key signal 166.
Subsequently, the content of the agreement contained in the related information signal 164 thus deencrypted is compared with the content of the built-in agreement of the receiver apparatus 161 by the agreement comparator circuit 169. According to the result of this comparison, it is judged whether the copy protection signal 179 is mixed into the descrambled video signal 176 or not.
When the content of the agreement contained in the related information signal 164 accords with the content of the built-in agreement of the receiver 161, the agreement comparator circuit 169 instructs the mixer 180 not to mix the copy protection signal 179 with the descrambler video signal 176 through the control signal 181. In this case, the outputted video signal 182 from the mixer 180 can be recorded into a recording medium by using a Video Tape Recorder (VTR) or the like, and it can be normally played back for watching and listening from the medium.
On the other hand, when the content of the agreement contained in the related information signal 164 does not accord with the content of the built-in agreement of the receiver apparatus 161, the agreement comparator circuit 169 instructs the mixer 180 to mix the copy protection signal 179 with the descrambled video signal 176 through the control signal 181. In this case, although the video signal 182 outputted from the mixer 180 can be recorded into a recording medium, the quality of the played-back video signal 182 from the recorded medium degrades greatly so that it is difficult or unable to be watched and listened.
An example of the copy-protection signal 179 is an amplitude-varying pulse signal, which is added to or mixed with a scanning signal in the vertical blanking period of a video signal. The amplitude of the pulse signal varies at individual fields or at a longer period than the that of the fields. In this case, an Automatic Gain Control (AGC) circuit in a reproducing or play-back system such as a VTR is affected by the amplitude-varying pulse signal and as a result, the level of the played-backed video signal from the recorded medium fluctuates so that it is difficult or unable to be watched and listened.
The video and audio signals 182 and 177 can be played back normally on a TV screen independent of the existence and absence of mixing of the copy-protection signal 179.
The above-described conventional receiver apparatus 161 shown in FIG. 1 has the following problems.
Firstly, the control or copy-protection bit needs to be additionally provided in the related information signal to prevent illegal copy of the programs or services. Therefore, to cope with the control or copy-protection bit thus added, some subsystem is essentially provided not only at the receiver side but also at the transmitter side. In other words, a dedicated bit for copy protection needs to be additionally provided in the control format at the transmitter side and at the same time, a dedicated process or processor needs to be additionally provided at the receiver side.
Thus, there is a problem that the circuit scale becomes large and the fabrication cost becomes high.
Second, the illegal-copy protection of the programs or services is implemented with the use of scrambling of the video, audio, and related information signals and mixing of the copy-protection signal 179 to the video signal 176 in the conventional receiver apparatus 161. Therefore, if the configuration of the conventional receiver apparatus 161 is redesigned so that the video, audio, and related information signals are processed in personal computers (PCs) with data storage media, not only the related information signal but also the video and audio signals may be freely supplied to the data bus of the PCs. This means that the video and audio signals can be digitally recorded or copied into the data storage media of the PCs.
Thus, there is another problem that the data signal excluding the video and audio signals is not selectively recorded into the data storage media of the PCs.
Accordingly, an object of the present invention is to provide a digital information processing system that ensures illegal-copy protection of video and audio signals without changing the structure or format of a stream of multiplexed video, audio, and data packets.
Another object of the present invention is to provide a digital information processing system that prevents video and audio signals from being outputted to a data processing path for a data storage medium.
Still another object of the present invention is to provide a digital information processing system in which a data signal excluding video and audio signals is selectively recorded into a data storage medium.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
A digital information processing system according to the present invention is comprised of (a) a packet stream processor for extracting a stream of multiplexed video, audio, and data packets that have been multiplexed in a source signal in conformity with the MPEG standard, and (b) a packet demultiplexer for demultiplexing the stream of the multiplexed packets by selecting one of the packets in the stream according to an assigned packet identifier (PID) of the packets.
The packet demultiplexer has a first output port electrically connected to video and audio signal decoders, and a second output port for digital processing such as storage.
When the selected one of the packets is a video or audio packet, the packet demultiplexer outputs the selected one of the packets through the first output port.
When the selected one of the packets is a data packet, the packet demultiplexer outputs the selected one of the packets through the second output port.
With the digital information processing system according to the present invention, the stream of multiplexed video, audio, and data packets that have been multiplexed in the source signal in conformity with the MPEG standard is extracted by the packet stream processor and then, the stream of the multiplexed packets is demultiplexed by the packet demultiplexer by selecting one of the packets in the stream according to an assigned or specified PID of the packets.
Further, when the selected one of the packets is a video or audio packet, the packet demultiplexer outputs the selected one of the packets through the first output port electrically connected to the video and audio signal decoders. When the selected one of the packets is a data packet, the packet demultiplexer outputs the selected one of the packets through the second output port for digital processing such as storage.
Thus, a data signal derived from the data packet is able to be digitally stored in a suitable storage medium through the second output port of the packet demultiplexer while video and audio signals derived from the video and audio packets are prevented from being outputted to a data processing path for a data storage medium. In other words, the data signal excluding the video and audio signals is selectively recorded into a data storage medium. The video and audio signals derived from the video and audio packets are played back or reproduced by the video and audio signal decoders.
As a result, illegal-copy protection of the audio and visual signals is ensured without changing the structure or format of the stream of the multiplexed video, audio, and data packets.
Further, because no change is required for the structure or format of the stream of the multiplexed video, audio, and data packets, the circuit scale of the digital information processing system does not become large and the fabrication cost thereof does not become high.
In a preferred embodiment of the system according to the present invention, the packet demultiplexer includes a packet-type information extractor for extracting a packet-type information included in the stream according to the assigned PID of the packets, and a packet-type checker for checking the type of the packets using the packet-type information extracted by the extractor and for selectively outputting the video and audio packets to the first output port and the data packet to the second output port.
As the packet-type informatioin, a packet map table (PMT is preferably used.
In another preferred embodiment of the system according to the present invention, the stream of the multiplexed packets has been scrambled and a descrambler for descrambling the scrambled stream of the multiplexed packets is provided.
In this case, the packet-type information extractor and the packet-type checker may be provided prior or next to the descrambler.
In still another preferred embodiment of the system according to the present invention, the source signal including the multiplexed video, audio, and data packets is transmitted by a transmitter. The packet stream processor receives the source signal and extracts the stream of the multiplexed packets from the received source signal.
In a further preferred embodiment of the system according to the present invention, a storage subsystem is provided for storing the source signal including the multiplexed video, audio, and data packets. The packet stream processor extracts the stream of the multiplexed packets from the storage subsystem.